The problem with just about every virtual desktop implementation is just that - they're virtual. This means that beyond the ability to move windows to specific desktops, you're still looking at exactly the same desktop, no matter what virtual desktop number you switched to. A mockup for GNOME Shell is trying to take the virtual out of virtual desktop.

activities are a central part of kde4 desktop and an understanding of how they work is critical if you want to fully use kde4.

Activities have an all or nothing approach. You can set your desktop to only have one activity in all virtual desktop and all your virtual desktop will be identical(because they will all look at the same activity) or you can set your desktop to have different activity for each desktop and all virtual desktops will be completely independent of one another and they wont be able share a wallpaper or icons or anything on the desktop.

kde4 currently ship with two activities,folder view and desktop.

Folder view activity gives the "traditional desktop", the kind of desktop you see in kde3 or windows. It is basically gives a dumb virtual desktop that shows the contents of ~/Desktop folder

activities are a central part of kde4 desktop and an understanding of how they work is critical if you want to fully use kde4.

Activities have an all or nothing approach. You can set your desktop to only have one activity in all virtual desktop and all your virtual desktop will be identical(because they will all look at the same activity) or you can set your desktop to have different activity for each desktop and all virtual desktops will be completely independent of one another and they wont be able share a wallpaper or icons or anything on the desktop.

kde4 currently ship with two activities,folder view and desktop.

Folder view activity gives the "traditional desktop", the kind of desktop you see in kde3 or windows. It is basically gives a dumb virtual desktop that shows the contents of ~/Desktop folder

Great, but each virtual desktop isn't independent. I can't set VD1 to be a Folder, VD2 to be a default Desktop, so on and so forth.

You can as long as you're in a recent KDE 4 release. (4.2 or higher, if I remember correctly)

In 4.2, you have to manually edit a config file because the UI wasn't ready by the string freeze, but in 4.3 and above, there's a "Different activity for each desktop" checkbox under SystemSettings --> Desktop --> Multiple Desktops.

For that matter, you can also use a separate activity for the MacOS-style dashboard via the dropdown box in SystemSettings --> Desktop --> Workspace.

Folder view activity gives the "traditional desktop", the kind of desktop you see in kde3 or windows. It is basically gives a dumb virtual desktop that shows the contents of ~/Desktop folder

And of course it's KDE so you do not need it to be simply a dumb desktop. As the folder view have access to and can use all the regular kio-slaves. You can have a virtual desktop showing remote files, with ftp:// or one of the other remote slaves. Or perhaps one containing files based on a metadata search with neopomuk://.